Liquid heating system

ABSTRACT

A liquid heating system and heat exchangers therefore are disclosed. Each heat exchanger comprises a right heating chamber having a right input port and a right output port, and a left heating chamber having a left input port and a left output port. A heating circuit is configured such that circulating heated supply fluid through the heating circuit heats target liquid present in the heating chambers. The system includes a plurality of heat exchangers including a first, a final, and a plurality of middle heat exchangers. The right and left heating chambers are connected such that target liquid flows into the right input port of the right chamber of the first heat exchanger and through each right chamber to the left chamber of the final heat exchanger, and then through each left chamber and through the left output port of the first heat exchanger to a hot liquid discharge.

This invention is in the field of liquid heating equipment, and in particular a system for heating varying volumes of liquid to selected temperatures.

BACKGROUND

In many industries a supply of hot water or other hot liquid is required for an operation on temporary basis. For example in some hydraulic fracturing operations on underground petroleum formations, large volumes of hot liquid comprising water mixed with various other products such as hydrocarbons, proppants and other additives are pumped down a well bore as part of the fracturing process. A continuous flow of liquid at a selected temperature for a period of time is required. The amount of liquid needed, and the selected temperature can vary from one situation to the next. Providing portable equipment that can be readily adapted to heat the required varying flow volumes of liquid to the varying selected temperatures is problematic.

Water from streams or ponds is often used, and this water often contains particulate matter which leaves sludge and contamination in the equipment used to heat the water. In some industries such contamination from one site must be cleaned out of the equipment so same is not transported to contaminate the next site.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a liquid heating system that overcomes problems in the prior art.

In a first embodiment the present invention provides a liquid heating system comprising a plurality of heat exchangers including a first heat exchanger, a final heat exchanger, and a plurality of middle heat exchangers. Each heat exchanger comprises a right heating chamber having a right input port and a right output port, and a left heating chamber having a left input port and a left output port. A heating circuit is connected to a source of heated supply fluid, and is configured such that circulating heated supply fluid through the heating circuit heats target liquid present in the right and left heating chambers. The right and left heating chambers are connected such that target liquid to be heated flows into the right input port of the right heating chamber of the first heat exchanger and through each right heating chamber to the left heating chamber of the final heat exchanger, and then through each left heating chamber and through the left output port of the first heat exchanger to a hot liquid discharge.

In a second embodiment the present invention provides a liquid heating system comprising a plurality of heat exchangers including a first heat exchanger, a final heat exchanger, and a plurality of middle heat exchangers. Each heat exchanger comprises a right heating chamber having a right input port and a right output port, and a left heating chamber having a left input port and a left output port. A heating circuit is connected to a source of heated supply fluid, and is configured such that circulating heated supply fluid through the heating circuit heats liquid present in the right and left heating chambers. The right input port of the first heat exchanger is connected to a source of target liquid to be heated, and the right output port of each of the first and middle heat exchangers is connected to the right input port of a next successive heat exchanger. The right input port of the final heat exchanger is connected to the right output port of a prior middle heat exchanger, and the right output port of the final heat exchanger is connected to the left input port of the final heat exchanger. The left output port of each of the final and middle heat exchangers is connected to the left input port of a next successive heat exchanger. The left input port of the first heat exchanger is connected to the left output port of a prior middle heat exchanger, and the left output port of the first heat exchanger is connected to a hot liquid discharge.

In a third embodiment the present invention provides a heat exchanger comprising an outer wall and end walls forming an enclosure. An inner dividing wall extends across the enclosure to form right and left heating chambers, the right heating chamber having a right input port and a right output port, and the left heating chamber having a left input port and a left output port. A heating circuit is adapted to be connected to a source of heated supply fluid and configured such that during operation heated supply fluid circulates through the outer wall and the inner dividing wall, and configured such that circulating heated supply fluid through the heating circuit heats liquid present in the right and left heating chambers.

The heat exchanger can be mounted with a fluid heating apparatus on a heating module that is portable and easily transported. The fluid heating apparatus can be a substantially self-contained combustion type fluid heater that can operate in a remote work site. In the system of the present invention each heat exchanger and fluid heating apparatus adds about the same amount of energy and temperature rise to the target liquid, and so operates efficiently, and minimizes the number of heating modules required.

The number of heating modules required can be calculated and portable equipment that can be readily adapted to heat the required varying flow volumes of water to the varying selected temperatures can be transported to the work site.

The heating chamber of the heat exchangers are open, without cross conduits or the like, and so can be cleaned of foreign material by providing closable cleaning apertures in each heating chamber.

In a fourth embodiment the present invention provides a heat exchanger apparatus comprising a heating chamber with an input port and an output port. A water jacket substantially encloses the heating chamber, the water jacket having a supply end extending substantially along a length of the heating chamber, and a return end extending substantially along a length of the heating chamber. A supply manifold extends along substantially a length of the supply end of the water jacket, the supply manifold defining a supply port adapted for connection to receive supply fluid from a circulating fluid heater, and a plurality of supply apertures along a length thereof connecting an interior of the supply manifold to an interior of the water jacket. A return manifold extends along substantially a length of the return end of the water jacket, the return manifold defining a return port adapted for connection to return supply fluid to the circulating fluid heater and a plurality of return apertures along a length thereof connecting an interior of the return manifold to the interior of the water jacket. A size of the supply apertures is selected such that a flow of supply fluid entering the supply port is restricted and such that resulting pressure in the supply manifold causes the supply fluid to flow along the length of the supply manifold and out through each supply aperture in the supply manifold, then through the interior of the water jacket around the heating chamber through a return aperture in the return manifold into the return manifold and through the return port.

DESCRIPTION OF THE DRAWINGS

While the invention is claimed in the concluding portions hereof, preferred embodiments are provided in the accompanying detailed description which may be best understood in conjunction with the accompanying diagrams where like parts in each of the several diagrams are labeled with like numbers, and where:

FIG. 1 is a top view of an embodiment of a liquid heating system of the present invention;

FIG. 2 is a front view of the embodiment of FIG. 1;

FIG. 3 is a schematic sectional front view of a heat exchanger of the embodiment of FIG. 1;

FIG. 4 is a schematic sectional end view of the heat exchanger illustrated in FIG. 3;

FIG. 5 is an end view of a heating module of the embodiment of FIG. 1 including the heat exchanger of FIG. 3 and a fluid heating apparatus;

FIG. 6 is a schematic illustration of the operation of a heating system of the prior art;

FIG. 7 is a schematic sectional view of a heat exchanger apparatus with a single heating chamber;

FIG. 8 is a schematic side view of the heat exchanger apparatus of FIG. 7;

FIG. 9 is a schematic view of the manifolds and water jacket of the heat exchanger apparatus of FIG. 7;

FIG. 10 is a schematic view of the manifolds and water jacket of a heat exchanger apparatus of the prior art.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIGS. 1 and 2 illustrate an embodiment of a liquid heating system 1 of the present invention. The liquid heating system 1 comprises a plurality of heat exchangers 3 including a first heat exchanger 3A, a final heat exchanger 3B, and a plurality of middle heat exchangers 3C. The heat exchanger 3 is schematically illustrated in FIGS. 3 and 4.

Each heat exchanger 3 comprises a right heating chamber 5 having a right input port 5A and a right output port 5B, and a left heating chamber 7 having a left input port 7A and a left output port 7B. The volume of the right heating chamber 5 is substantially equal to the volume of the left heating chamber 7.

The right and left input ports 5A, 7A are located in lower portions of the corresponding right and left heating chambers 5, 7 and the right and left output ports 5B, 7B are located in upper portions of the corresponding right and left heating chambers 5, 7. Thus cooler liquid enters the input ports 5A, 7A at the bottom of the chamber where same is heated as it passes through the chamber to the output ports 5B, 7B located at the top of the opposite end of the chamber. The hottest liquid in the chamber will be at the top of the chamber and thus will flow out of the output ports 5B, 7B.

The terms “right” and “left” are used for convenience of reference only to differentiate the heating chambers for the purposes of the present description.

A heating circuit 9 is connected to a source of heated supply fluid, and is configured such that circulating heated supply fluid 11 through the heating circuit 9 heats liquid present in the right and left heating chambers 5, 7. In the illustrated system 1, each heat exchanger is mounted on a heating module 13, illustrated in FIG. 5, that includes a fluid heating apparatus 15 operative to provide the source of heated supply fluid. The heating module 13 is portable and easily moved from one job site to the next, and includes any pumps, fuel tanks, electrical power systems, and the like necessary to operate, control, and circulate the heated supply fluid 11 through the fluid heating apparatus 15 and the heat exchanger 3. The fluid heating apparatus 15 is typically provided by a substantially self-contained combustion type fluid heater that does not require external electrical power and so can be conveniently set up and operated at a remote work site.

The illustrated heat exchanger 3 includes an outer wall 17 and end walls 19 forming an enclosure, and an inner dividing wall 23 extending across the enclosure to form the right and left heating chambers 5, 7, and the heating circuit 9 is configured such that heated supply fluid 11 circulates through the outer wall 17 and the inner dividing wall 23. The illustrated heating circuit 9 includes a supply input line 25 connected to a supply manifold 27 that distributes the heated supply fluid 11 along a length of the heat exchanger 3 through manifold holes 29. The heated supply fluid 11 then flows through a water jacket 31 around a first side of the outer wall 17, then up the inner dividing wall 23, back down the inner dividing wall 23, and up the second side of the outer wall 17 through a return manifold 28 to the return line 33 and back to the fluid heating source 15.

In the system 1 of the present invention the right and left heating chambers 5, 7 are connected such that the target liquid 35 that is to be heated flows into the right input port 5A of the right heating chamber 5 of the first heat exchanger 3A and through each right heating chamber 5 of the first, middle, and final heat exchangers 3A, 3C, 3B to the left heating chamber 7 of the final heat exchanger 3B, and then through each left heating 7 chamber of the final, middle, and first heat exchangers 3B, 3C, 3A and through the left output port 7B of the first heat exchanger 3A to a hot liquid discharge 37. Direction of target liquid flow is indicated by arrows between the heat exchangers 3 in FIGS. 3 and 4.

The right input port 5A of the first heat exchanger 3 a is connected to a source 39 of target liquid 35 to be heated, and then right output ports 5B and right input ports 5A are connected together such that target liquid 35 flows from the right input port 5A of the first heat exchanger 3A through each right heating chamber of the first and middle heat exchangers 3A, 3C to the right heating chamber 5 of the final heat exchanger 3B. The right output port 5B of the final heat exchanger 3B is then connected to the left input port 7A of the final heat exchanger 3B and left output ports 7B and left input ports 7A are connected together such that the target liquid 35 flows from the right output port 5B of the final heat exchanger 3B through each left heating chamber 7 of the final and middle heat exchangers 3B, 3C to the left heating chamber 7 of the first heat exchanger 3A and out the output port 7B thereof.

In the system 1 the temperature of the target liquid 35 increases in each chamber such that the temperature of the target liquid 35 at the output port 5B or 7B of any heating chamber 5, 7 is greater than the temperature thereof at the input port 5A or 7A of that same heating chamber. Thus since the target liquid 35 flows through all the right heating chambers 5 before entering the left heating chamber 7 of the final heat exchanger 3B and then flowing through all the left heating chambers 7 in reverse order, it can be seen that in each heat exchanger 3 of the system 1, the target liquid 35 in the right heating chamber 5 will have a temperature that is lower than the temperature of the target liquid in the left heating chamber 7 thereof.

As well, the lowest temperature of the target liquid 35 will be when entering the system 1 at the input port 5A of the right heating chamber 5 of the first heat exchanger 3A, with some temperature increase in each heating chamber between the input and output ports thereof until the target liquid 35 exits the system 1 to the hot liquid discharge 37 at the maximum temperature achieved.

In the prior art at a typical work site where it is required to heat a target liquid, as schematically illustrated in FIG. 6 a number of similar conventional liquid heating units 113 would be connected together, the number selected to achieve the desired temperature increase at the required flow rate. The target liquid 135 enters the first unit at a first temperature T1, and leaves the first unit at temperature T2 and enters the second unit at that temperature T2, leaves the second unit at temperature T3 and enters the third unit at that temperature T3, leaves the third unit at temperature T4 and enters the fourth unit at that temperature T4 and leaves the fourth unit at the desired temperature T5.

It is known that the rate of heat transfer from one liquid or like source to another liquid or like target decreases as the temperature gradient between the source and the target decreases.

Thus in the conventional system of FIG. 6, in the first conventional liquid heating unit the supply fluid will enter the heat exchanger of the unit at a supply temperature TS, heat will be absorbed from the supply fluid relatively quickly by the cold target liquid at temperature T1 and the supply fluid returns from the heat exchanger 103 to the fluid heater 115 at a return temperature TR significantly less than the supply temperature TS.

Then in the second conventional liquid heating unit, the supply fluid will again enter the heat exchanger of the unit at a temperature TS, heat will be absorbed less quickly by the target liquid at the higher temperature T2 and the supply liquid returns from the heat exchanger 103 to the fluid heater 115 at return temperature TR′ that is higher than the return temperature TR of the supply fluid in the first unit. Similarly on through the rest of the conventional liquid heating units 113, such that in the schematic illustration of FIG. 6, TR<TR′<TR″<TR″′.

The amount of energy added by each conventional liquid heating unit 113 to the target liquid is proportional to the difference between the supply temperature TS and the return temperature TR of the unit. Thus each successive conventional liquid heating unit 113 transfers less energy than the prior unit.

In contrast in the system 1 of the present invention, since the volume of the right and left heating chambers is substantially the same, the average temperature of the target liquid 35 in each heat exchanger 3 is the average of the temperature RT of the target, liquid in the right heating chamber and the temperature LT of the target liquid in the left heating chamber.

Thus in the first heat exchanger 3A the temperature RT of the target liquid in the right heating chamber 5 that is just entering the system 1 is the coldest of any heating chamber in any of the heat exchangers 3, while the temperature LT of the target liquid in the left heating chamber 7 that is just leaving the system 1 is the hottest of any heating chamber in any of the heat exchangers 3. The average temperature in the first heat exchanger 3A is thus (RTA+LTA)/2.

In the next in line middle heat exchanger 3C′, the temperature RT of the target liquid in the right heating chamber 5 is higher than the temperature in the prior right heating chamber 5 of the first heat exchanger 3A, and the temperature LT of the target liquid in the left heating chamber 5 is lower than the temperature in the subsequent left heating chamber 7 of the first heat exchanger 3A, and the average temperature of the target liquid in heat exchanger 3C′ is about the same as the average temperature of the target liquid in first heat exchanger 3A.

This temperature relationship carries on all through the system 1 from one heat exchanger to the next. In the final heat exchanger 3B, the temperature RT of the target liquid in the right heating chamber 5 is only one temperature step less than temperature LT of the target liquid in the left heating chamber 7. The target liquid 35 at this point is just about to turn and return along the left heating chambers 7 of the string of heat exchangers, and the temperature thereof has increased by about one half of the total increase required between the temperature of the target liquid entering the system and the temperature of the target liquid leaving the system, and is therefore at an average temperature of about (RTA+LTA)/2, the same as in the first heat exchanger 3A.

The temperature of the target liquid in each heating chamber 5, 7 will increase between the input port and the output port, however generally speaking the above described temperature relationship will be present in each heat exchanger 3. Thus the temperature gradient between the supply temperature TS of the supply fluid entering each heat exchanger 3 and the average temperature of the target fluid in the right and left heating chambers 5, 7 of the heat exchanger 3 will be about the same in each heat exchanger. The return temperature TR of the supply fluid leaving each heat exchanger and returning to the fluid heating source 15 will also be about the same, and so the amount of energy added by each heat exchanger 3 and fluid heating source 15 to the target liquid is about the same.

With each heat exchanger 3 and fluid heating source 15 adding the same amount of energy, the number of heating modules 13 in the system 1 of the invention is reduced compared to the number of conventional liquid heating units 113 required, where each successive conventional liquid heating unit 113 transfers less energy than the prior unit.

The heat exchangers of the illustrated system 1 also define cleaning apertures 41 in the right and left heating chambers 5, 7, and removable covers 43 on the cleaning apertures. The heating chambers 5, 7 are open with substantially smooth walls which can be readily cleaned of accumulated residue, sludge, sediment, and like particles of material that can result from, for example, using unclean water from rivers, ponds, and the like as is sometimes desirable in remote work sites.

The cleaning apertures 41 schematically illustrated in FIG. 4 are defined in the top of the outer wall 17 but same could also be defined in an end wall 19 as illustrated in FIG. 3, where an upper cleaning aperture 41A and a lower drain aperture 41B in each of the right and left heating chambers 5, 7 would facilitate cleaning of foreign material from the heating chamber 5, 7.

It is contemplated that 20-30 heating modules 13 could be practically connected in the system 1 of the present invention to provide a wide range of heating capacities for a wide range of water flow volumes and desired target liquid temperatures. The independent heating modules are conveniently transported and connected by simple conduits and connectors such that assembly at a work site is readily accomplished.

FIGS. 7-9 schematically illustrate the operation of the water jacket 31 and manifolds 27, 28 of FIG. 3 in use on a heat exchanger apparatus 203 that has only a single heating chamber 205 with an input port 205A and an output port 205B. A water jacket 231 substantially encloses the heating chamber 205. The water jacket 231 will in some applications enclose the ends of the heating chamber 205 as well as the walls thereof, or in other applications the ends will be covered by an insulating layer. The illustrated water jacket 231 has a supply end 231A extending the length L of the heating chamber 205, and a return end 231B extending the length L of the heating chamber 205.

A supply manifold 227 extends along substantially a length of the supply end 231A of the water jacket 231. The supply manifold 227 defines a supply port 227A adapted for connection to a supply line 225 to receive supply fluid 211 from a circulating fluid heater 215, and a plurality of supply apertures 229 along a length thereof connecting an interior of the supply manifold 227 to an interior of the water jacket 231.

A return manifold 228 extends along substantially a length of the return end 231B of the water jacket 231. The return manifold defines a return port 228A adapted for connection to a return line 233 to return supply fluid 211 to the circulating fluid heater 215 and a plurality of return apertures 230 along a length thereof connecting an interior of the return manifold to the interior of the water jacket 231.

The size of the supply apertures 229 is selected such that a flow of supply fluid 211 entering the supply port 227A is restricted and such that resulting pressure in the supply manifold 227 causes the supply fluid 211 to flow along the length of the supply manifold 227 and out through each supply aperture 229 in the supply manifold, then around the heating chamber 205 through one of the return apertures 230 into the return manifold 228 and through the return port 228A to the return line 233. The supply port 227A and return port 228A are located substantially at a mid-point of the length of the corresponding supply and return manifolds 227, 228 to provide even fluid flow from each end of the manifolds.

The effect of the manifolds 227, 228 on the flow of supply fluid through the water jacket 231 is schematically illustrated in FIG. 9. The back pressure in the supply manifold 227 ensures that supply fluid 211 moves down the length of the supply manifold 228 and out each supply aperture 229, more or less equally through each. The flow of supply liquid 211 is indicated by the arrows. Because the return manifold 228 on the opposite end of the water jacket 231 also has return apertures 230 along the length thereof the supply liquid 211 will flow generally from a supply aperture 229 to an opposite return aperture 230 such that a substantially equal flow of supply fluid 211 is present along the length of the water jacket 231 from the supply end 231A thereof to the return end 231B thereof.

The total area of the supply apertures 229 is generally less than a total area of the return apertures 230 such that there is little resistance to the flow of supply liquid 211 into the return manifold 228. Thus where the number of supply apertures 229 is the same as the number of return apertures 230, and where each supply aperture 229 has substantially the same area and each return aperture 230 has substantially the same area, and the area of each return aperture 230 will be greater than the area of each supply aperture 230. Conveniently the return apertures 230 will simply be somewhat larger than the supply apertures 229, but the number of apertures 229, 230 could vary and a similar result obtained by sizing the apertures accordingly.

This even flow provides an even temperature across the length L of the water jacket 231, decreasing from the supply end 231A to the return end 231B as heat is transferred from the supply fluid 211 to a target liquid in the heating chamber 205. Thus the entire area of the water jacket 231 is substantially at the same temperature gradient and is exposed to the heating chamber 205.

Heat transfer from the water jacket 231 to the heating chamber 205 is increased compared to a typical prior art water jacket 331 illustrated in FIG. 10, where the supply fluid 311 enters the water jacket 331 directly through a supply line 325 and leaves directly through a return line 333. The supply fluid 311 enters the middle of the supply end 331A of the water jacket 331 and then moves naturally toward the return line 333 in the middle of the opposite return end 331B thereof, generally as indicated by the arrows. As there are no inlets or outlets near the outer regions 334 of the water jacket 331 removed from the supply line 325 and return line 333, there is little flow of supply liquid 311 in the outer regions 334 of the water jacket 331. The temperature of the outer regions 334 is therefore significantly less than the central regions 336 of the water jacket 331 through which the supply liquid 311 predominantly flows, and heat transfer efficiency is reduced.

In the heat exchanger apparatus 3 of FIGS. 3 and 4 as discussed above the heating chamber is divided into a right heating chamber 5 having a right input port 5A and a right output port 5B, and a left heating chamber 7 having a left input port 7A and a left output port 7B, and the water jacket 31 includes similar supply and return manifolds 27, 28 and is configured to heat a target liquid in both the right and left heating chambers 5, 7 in a similar even efficient manner.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous changes and modifications will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all such suitable changes or modifications in structure or operation which may be resorted to are intended to fall within the scope of the claimed invention. 

What is claimed is:
 1. A liquid heating system comprising: a plurality of heat exchangers including a first heat exchanger, a final heat exchanger, and a plurality of middle heat exchangers, each heat exchanger comprising: a right heating chamber having a right input port and a right output port; a left heating chamber having a left input port and a left output port; a heating circuit connected to a source of heated supply fluid, and configured such that circulating heated supply fluid through the heating circuit heats target liquid present in the right and left heating chambers; wherein the right and left heating chambers are connected such that target liquid to be heated flows into the right input port of the right heating chamber of the first heat exchanger and through each right heating chamber to the left heating chamber of the final heat exchanger, and then through each left heating chamber and through the left output port of the first heat exchanger to a hot liquid discharge.
 2. The system of claim 1 wherein the right input port of the first heat exchanger is connected to a source of target liquid to be heated, and right output ports and right input ports are connected together such that target liquid to be heated flows from the right input port of the first heat exchanger through each right heating chamber of the first and middle heat exchangers to the right heating chamber of the final heat exchanger; wherein the right output port of the final heat exchanger is connected to the left input port of the final heat exchanger and left output ports and left input ports are connected together such that target liquid to be heated flows from the right output port of the final heat exchanger through each left heating chamber of the final and middle heat exchangers to the left heating chamber of the first heat exchanger.
 3. The system of claim 1 wherein the right and left input ports are located in lower portions of the corresponding right and left heating chambers, and the right and left output ports are located in upper portions of the corresponding right and left heating chambers.
 4. The system of claim 1 wherein each heat exchanger is mounted on a heating module, and wherein the heating module comprises a fluid heating apparatus operative to provide the source of heated supply fluid.
 5. The system of claim 1 wherein at least one heat exchanger comprises an outer wall and end walls forming an enclosure and an inner dividing wall extending across the enclosure to form the right and left heating chambers, and wherein the heating circuit is configured such that heated supply fluid circulates through the outer wall and the inner dividing wall.
 6. The system of claim 1 wherein at least one heat exchanger defines cleaning apertures in the right and left heating chambers, and removable covers on the cleaning apertures.
 7. The system of claim 6 wherein the cleaning apertures are defined in at least one of an end wall and the outer wall.
 8. The system of claim 6 comprising an upper cleaning aperture and a lower drain aperture in each of the right and left heating chambers.
 9. The system of claim 1 wherein a volume of the right heating chamber is substantially equal to a volume of the left heating chamber.
 10. A liquid heating system comprising: a plurality of heat exchangers including a first heat exchanger, a final heat exchanger, and a plurality of middle heat exchangers, each heat exchanger comprising: a right heating chamber having a right input port and a right output port; a left heating chamber having a left input port and a left output port; a heating circuit connected to a source of heated supply fluid, and configured such that circulating heated supply fluid through the heating circuit heats liquid present in the right and left heating chambers; wherein the right input port of the first heat exchanger is connected to a source of target liquid to be heated, and the right output port of each of the first and middle heat exchangers is connected to the right input port of a next successive heat exchanger; wherein the right input port of the final heat exchanger is connected to the right output port of a prior middle heat exchanger, and the right output port of the final heat exchanger is connected to the left input port of the final heat exchanger; wherein the left output port of each of the final and middle heat exchangers is connected to the left input port of a, next successive heat exchanger; wherein the left input port of the first heat exchanger is connected to the left output port of a prior middle heat exchanger, and the left output port of the first heat exchanger is connected to a hot liquid discharge.
 11. A heat exchanger comprising: an outer wall and end walls forming an enclosure; an inner dividing wall extending across the enclosure to form right and left heating chambers, the right heating chamber having a right input port and a right output port, and the left heating chamber having a left input port and a left output port; a heating circuit adapted to be connected to a source of heated supply fluid and configured such that during operation heated supply fluid circulates through the outer wall and the inner dividing wall, and configured such that circulating heated supply fluid through the heating circuit heats liquid present in the right and left heating chambers.
 12. The heat exchanger of claim 11 comprising cleaning apertures defined in the right and left heating chambers, and removable covers on the cleaning apertures.
 13. The heat exchanger of claim 12 wherein the cleaning apertures are defined in at least one of an end wall and the outer wall.
 14. The heat exchanger of claim 12 comprising an upper cleaning aperture and a lower drain aperture in each of the right and left heating chambers.
 15. The heat exchanger of claim 11 wherein the right and left input ports are located in lower portions of the corresponding right and left heating chambers, and the right and left output ports are located in upper portions of the corresponding right and left heating chambers.
 16. The heat exchanger of claim 11 wherein a volume of the right heating chamber is substantially equal to a volume of the left heating chamber.
 17. A liquid heating system comprising a plurality of heat exchangers of claim 11, the system including a first heat exchanger, a final heat exchanger, and a plurality of middle heat exchangers, and wherein the right and left heating chambers are connected such that target liquid to be heated flows into the right input port of the right heating chamber of the first heat exchanger and through each right heating chamber to the left heating chamber of the final heat exchanger, and then through each left heating chamber to the left output port of the first heat exchanger.
 18. The system of claim 17 wherein each heat exchanger is mounted on a heating module, and wherein the heating module comprises a fluid heating apparatus operative to provide the source of heated supply fluid.
 19. A heat exchanger apparatus comprising: a heating chamber with an input port and an output port; a water jacket substantially enclosing the heating chamber, the water jacket having a supply end extending along substantially a length of the heating chamber, and a return end extending along substantially the length of the heating chamber; a supply manifold extending along substantially a length of the supply end of the water jacket, the supply manifold defining a supply port adapted for connection to receive supply fluid from a circulating fluid heater, and a plurality of supply apertures along a length thereof connecting an interior of the supply manifold to an interior of the water jacket; a return manifold extending along substantially a length of the return end of the water jacket, the return manifold defining a return port adapted for connection to return supply fluid to the circulating fluid heater and a plurality of return apertures along a length thereof connecting an interior of the return manifold to the interior of the water jacket; wherein a size of the supply apertures is selected such that a flow of supply fluid entering the supply port is restricted and such that resulting pressure in the supply manifold causes the supply fluid to flow along the length of the supply manifold and out through each supply aperture in the supply manifold, then through the interior of the water jacket around the heating chamber through a return aperture into the return manifold and through the return port.
 20. The apparatus of claim 19 wherein a total area of the supply apertures is less than a total area of the return apertures.
 21. The apparatus of claim 20 wherein the number of supply apertures is the same as the number of return apertures, each supply aperture has substantially the same area, each return aperture has substantially the same area, and wherein the area of the return apertures is greater than the area of the supply apertures.
 22. The apparatus of claim 19 wherein the supply end and the return end of the water jacket extend substantially a length of the heating chamber.
 23. The apparatus of claim 19 wherein the supply port and return port are located substantially at a mid-point of a length of the corresponding supply and return manifolds.
 24. The apparatus of claim 19 wherein the heating chamber is divided into a right heating chamber having a right input port and a right output port, and a left heating chamber having a left input port and a left output port, and wherein the water jacket is configured to heat a target liquid in both the right and left heating chambers. 